This invention relates to a process and catalyst composition for the epoxidation of olefins by hydrogen peroxide.
The epoxides constitute a class of compounds of which the industrial importance is measured by the tonnages produced and by the diversity of their applications in the field of urethanes, glycols, surface-active agents, plasticizers and numerous other derivatives.
While many specific methods for epoxidizing olefins are known, the most prominent of these methods can generally be divided into four basic types. For example, the oldest industrial technique for the epoxidation of double bonds is the process known as the chlorohydrin process. In the chlorohydrin process an olefin is reacted with chlorine in an alkaline medium. The yields (based on the chlorine) are unsatisfactory. This process also gives rise to the simultaneous formation of considerable quantities of chlorinated by-products, both inorganic and organic, which products are unsuitable for any known purpose. The disposal of these by-products involves problems of such magnitude that this process may eventually be abandoned.
The second type of epoxidation method is generally limited to the epoxidation of ethylene. In accordance with this method ethylene is epoxidized with good yields in the vapor phase by means of molecular oxygen over a catalyst on a silver base. However, this technique is not very useful for the higher carbon olefins because of its lack of selectivity.
A third and more recent type of epoxidation process is characterized by the use of organic hydroperoxides. In accordance with processes of this type an olefin is epoxidized catalytically in an organic medium containing an organic hydroperoxide oxidant. In addition to employing a relatively expensive organic hydroperoxide as an oxidant, it is also a characteristic disadvantage of these processes that the epoxide formation is accompanied by the formation in an equivalent or even greater amount of an alcohol derived from the organic hydroperoxide employed in the process. Consequently, the commercial viability of these processes is always influenced by the ability to economically dispose of the alcohol by-product in addition to the epoxide.
Accordingly, new methods of access to the olefin oxides have been sought which are more direct, more selective, and especially are free from the problem of byproducts.
This has led to the development of the fourth type of epoxidation process which is characterized by the use of hydrogen peroxide as the oxidant.
Hydrogen peroxide is in principle a desirable reagent, for the very reason of its oxidizing non-polluting nature. However its reactivity towards olefins is weak or non-existent in the absence of an activating agent which enables a more active peroxy compound to be formed in-situ. Different processes of epoxidation have therefore been proposed using, for example, organic per-acids such as performic, peracetic or perpropionic acids (see, for example, Belgium Pat. No. 535,068). Nevertheless, because of the instability of the epoxides in acid medium, such processes are particularly difficult to put into practice.
It has been proposed to use oxides, oxyacids, or peroxyacids derived from metals such as arsenic, antimony, bismuth, and tungsten (see for example U.S. Pat. No. 3,993,673, European Patent Application Publication Nos. 0 008 496 and 0 009 262; and British Pat. No. 754,359). However, when such metal catalysts are employed in conjunction with aqueous hydrogen peroxide, the hydrogen peroxide is either rapidly decomposed or the rate of epoxidation is uneconomical. Thus, in an aqueous medium the addition of a metallic catalyst can be self-defeating. Consequently, for optimum performance when using these catalysts an important requirement of the system is that the hydrogen peroxide be anhydrous. However economic mass production of hydrogen peroxide has become possible owing to developments in the oxidation of secondary alcohols or quinone compounds. These routes to hydrogen peroxide synthesis as practiced commercially ultimately produce dilute aqueous solutions of hydrogen peroxide. Consequently, the cheapest commercially available hydrogen peroxide is generally sold as a 35-40% by weight, aqueous solution thereof. If one has to remove the water from these solutions for use in anhydrous sytems, the effective cost of the hydrogen peroxide is increased substantially, thereby increasing the cost of any system requiring the use of anhydrous hydrogen peroxide. It would therefore be economically beneficial to develop a catalytic system which can operate in a medium containing sufficient water such that commercially available aqueous solutions of hydrogen peroxide could be used directly without concentration and/or purification.
U.S. Pat. No. 3,778,451 discloses the epoxidation of olefins in an organic solvent medium containing hydrogen peroxide, transition metal compounds, i.e., those of molybdenum, tungsten, vanadium, niobium, tantalum, uranium or rhenium, and a nitrogenous organic base. The organic solvent employed includes alcohols, glycols, esters, linear or cyclic ethers, and certain weak carboxylic acids. However the hydrogen peroxide is employed in substantially anhydrous and concentrated form e.g. contains less than 10%, preferably less than 1% water to limit the production of undesirable hydroxylated by-products.
British Pat. No. 1,399,639 discloses the use of a fluorinated ketone, e.g., hexafluoroacetone, or hydrate thereof as a catalyst which can be used in excess quantities to function also as a solvent, or hexafluoroisopropanol (HFIP) as the solvent. However, this patent does not disclose the use of the phenolic Co-catalyst II of the present invention nor does it disclose the use of any catalyst in conjunction with the specific Group V element containing co-catalysts disclosed herein. Moreover, a majority of reaction times disclosed therein range from about 4 to as high as 270 hours, generally between 5 and 18 hours.
Similarly, it has been reported that the reaction product of hexafluoroacetone with concentrated hydrogen peroxide, i.e., 2-hydroperoxy-hexafluoro-2-propanol, in combination with 30% to 90% H.sub.2 O.sub.2 (latter gives best results) provides for the catalytic epoxidation of alkenes (see R. P. Heggs, JACS, 2484-2486, 1979). Later, the same Journal reported on arsenated polystyrenes as catalysts for the epoxidation of olefins by aqueous hydrogen peroxide (Jacobson et al, JACS 6946-6950, 1979).
U.S. Pat. No. 4,024,165 discloses that the olefin epoxidation process with hydrogen peroxide can be carried out in a fluorinated alcoholic solvent in which all the reactants and catalysts are soluble by using as the catalyst composition a soluble transition metal compound (the disclosed transition metals being limited to molybdenum, tungsten, vanadium, niobium, tantalum, uranium, or rhenium) and a soluble nitrogen-containing compound. In this patent the hydrogen peroxide is present as an aqueous solution, usually 50% by weight (see column 3, lines 19-27). However, the reaction times reported in this reference associated with yields of any significance of olefin oxide range from about 5 to about 8 hours. At reaction times below about 5 hours, the yield of olefin oxide drops substantially and in some instances no reaction at all takes place. Moreover, when either the transition metal compound or the nitrogen containing compound is eliminated from the catalyst composition, yields of olefin oxide also drop significantly. (Compare Examples 1 and 2 wherein Example 2, elimination of the nitrogen containing compound results in the undesirable polymerization of the olefin oxide; compare also Examples 21 and 24 wherein elimination of the transition metal compound in Example 24 drops the yield from 70 to 35%).
U.S. Pat. No. 4,257,948 discloses a process for epoxidizing acyclic, cyclic, or polycyclic olefins using hydrogen peroxide and a hexachloroacetone catalyst. This patent does not disclose the use of any transition metal catalysts or any other catalyst.
U.S. Pat. No. 3,993,673 discloses a process for epoxidizing olefins in the presence of an arsenic catalyst essentially free of tungsten, molybdenum, vanadium and chromium, a hydrogen peroxide oxidant, and an inert organic solvent. Suitable organic solvents include ethers, esters, alcohols, glycols, chlorinated solvents including chlorinated hydrocarbons, and chlorinated aromatics (e.g., chlorobenzene, o-dichlorobenzene, chloroform, and 1,1,2,2-tetra chloro ethane). Although the "hydrogen peroxide can be used in aqueous solutions . . . it is preferred to use less water than more" (column 3, lines 43-47). Such chlorinated solvents are not disclosed in this reference to possess any catalytic activity, nor do any of the disclosed chlorinated materials include the phenolic co-catalysts of the present invention.
European patent application Publication No. 0 008 496 discloses a polymer supported arsenic heterogeneous catalyst and a process for using the same to oxidize ketones, esters, and olefins in the presence of hydrogen peroxide. When dilute aqueous solutions of hydrogen peroxide are employed as the oxidant, a water immiscible solvent must be employed to avoid contact and hydrolysis of the oxidation products with water. In this embodiment, the substrate to be oxidized as well as the oxidation product are dissolved in the water immiscible solvent creating a two phase organic/aqueous system wherein the hydrogen peroxide is present in the aqueous phase. The polymer supported arsenic catalyst, functioning as a phase transfer catalyst, concentrates at the phase boundary whereat the arsono groups in the polymer are converted by contact with the hydrogen peroxide to perarsono, and this group on contacting the compound to be oxidized in the organic phase oxidizes it with regeneration of the arsono group. Thus, while suitable water immiscible solvents are disclosed as including chlorinated hydrocarbons, such as chloroform, these solvents are employed solely for their water immiscible property and not for any promoting effect on the arsenic catalyst.
Other phase transfer catalytic systems are disclosed in U.S. Pat. No. 3,992,432 and British Pat. No. 1,324,763.
European patent application Publication No. 0 009 262 discloses the in-situ production of hydrogen peroxide and use of the resulting hydrogen peroxide directly in arsenic catalyzed epoxidation reactions of olefins. The in-situ production of hydrogen peroxide as well as the epoxidation reaction can be conducted in the presence of aliphatic or cycloaliphatic ethers, aliphatic esters, chlorinated alkanes, chlorinated arenes or sulfolane. None of the solvents disclosed include the phenolic Co-catalysts II of the present invention.
British Patent Specification No. 1,452,730 discloses a process for epoxidizing olefins using acetic acid as the catalyst in the presence of aqueous hydrogen peroxide and an inert, chlorinated aliphatic hydrocarbon solvent such as chloroform. The solvent limits the hydrolysis of epoxidized products by the aqueous H.sub.2 O.sub.2 /acetic acid solution. Although, the exact mechanism by which this is achieved is not disclosed, it is known that the chlorinated hydrocarbon solvents are water immiscible. Consequently, it is believed that these solvents shield, to varying degrees, the epoxidized product from contact with the aqueous phase by solubilizing the epoxidized product therein. The phenolic Co-catalyst II of the present invention is not dependent on water immiscibility for its promoting effect, and in fact is generally water miscible due to the polar hydroxy group.
Other patents which disclose acid catalysis include U.S. Pat. No. 3,248,404 (discloses aliphatic and aromatic mono carboxylic acids and their halogenated derivatives as catalysts, e.g., acetic acid, chloroacetic acid, and benzoic acid in conjunction with a sequestering agent having acid complex forming properties); British Pat. No. 1,143,433 (discloses a carboxylic acid cation exchange resin as a catalyst); U.S. Pat. No. 2,870,171 (discloses the use of a tungsten acid deposited on an inert support as catalyst); and British Patent Specification No. 754,359 (discloses the use of inorganic peracids catalysts such as the peracids of tungsten, vanadium, and molybdenum as well as heteropoly acids such as the heteropolytungstic acids of arsenic, antimony or bismuth).
British Pat. No. 1,302,441 is directed to a process for epoxidizing olefins using hydrogen peroxide and a two component catalyst composition comprising as a first component an organo tin compound having at least one hydroxyl group or coordination group which can be converted to a hydroxyl group in the presence of water or hydrogen peroxide, and as a second component, at least one compound containing at least one of molybdenum, tungsten, vanadium, selenium, and boron. Suitable solvents for the reaction include alcohols, e.g., straight chain alcohols, polyhydric alcohols, and cyclic alcohols, as well as epoxides, ketones, and furfurals. Halogenated solvents are not disclosed. While this patent does not require the use of anhydrous or substantially anhydrous hydrogen peroxide, it will be noted that when aqueous solutions of hydrogen peroxide are employed, the reaction times vary from 4 to 24 hours. For example, at 90% concentrations of H.sub.2 O.sub.2 in water (Examples 1, 2 and 4-14) the average reaction time is about 13 hours. However at 70% H.sub.2 O.sub.2 in water (Examples 15-18) the reaction time is always 20 hours. In contrast when no water is employed with the H.sub.2 O.sub.2 (Examples 35-52) reaction times are measured in minutes (e.g. 60 to 360 minutes). Thus, the activity of the catalyst composition of this patent is reduced substantially even at relatively high H.sub.2 O.sub.2 concentrations in water.
Further, it was reported in the Chemical and Engineering news issue of December 11, 1978 on page 24 that both Produits Chemique Ugine Kuhlmann and Union Carbide have each directly oxidized propylene with hydrogen peroxide using an arsenic catalyst. In the former process, hydrogen peroxide of a 70% concentration is employed and for the latter 90% concentration (the author notes that the latter catalyst is adversely affected by the presence of water), with no mention of whether any additional inert diluent or solvent is present.
In summary, substantially all of the disclosures on the epoxidations of olefins to olefin epoxides, particularly propylene to propylene oxide, in which aqueous hydrogen peroxide is used directly in contact with the olefin in either the presence or absence of transition metal catalysts, have eluded commercial development due to one or more economic disadvantages. For example, the aqueous hydrogen peroxide used typically must be substantially above 30% in concentration, and/or the selectivity to propylene oxide is low, or the amount of time required for the reaction is too long. For these reasons, a practical route for direct epoxidation of olefins by aqueous hydrogen peroxide is a long-standing goal in oxidation chemistry. More specifically, it would be extremely economically advantageous to provide a process for epoxidizing olefins using extremely short reaction times while simultaneously achieving comparable or better yields obtainable with prior art techniques particularly, in a dilute aqueous system of H.sub.2 O.sub.2. Extremely short reaction times enable one to employ simpler plant designs by drastically reducing the size of the reaction vessel. Extremely short reaction times also permit one to employ simplified product separation techniques, such as conventional product flash-off procedures, wherein product is continually vaporized directly from the reaction medium, recovered and isolated. If the reaction time is too long, the amount of product vaporized at any given time would be too small to make this technique economically feasible. The ability to use dilute aqueous solutions of H.sub.2 O.sub.2 would further increase the flexibility and improve the economics of the process.
Accordingly, there has been a continuing search for processes and catalyst compositions that permit the use of dilute aqueous H.sub.2 O.sub.2 containing reaction mixtures, where it is advantageous to do so, and which substantially reduce the epoxidation reaction time without sacrificing olefin oxide yield to the point where the process becomes uneconomical.
One response to this search is provided in commonly assigned U.S. patent application Ser. No. 387,341, filed June 11, 1982, of M. G. Romanelli, which is directed to a process for epoxidizing olefins with hydrogen peroxide in the presence of a catalyst composition comprising as a Co-catalyst I, at least one Group V element containing compound, said Group V element being selected from As, P, Sb, and Bi (e.g., phenyl arsonic acid), and as a Co-catalyst II at least one fluorinated compound containing an oxygenated functional group such as hexafluoroisopropanol. The scope of the fluorinated oxygenated compounds disclosed in this application, however, is limited to those compounds wherein the oxygenated functional group is located on a saturated aliphatic carbon and not an aromatic carbon. While the invention disclosed in this application represents a substantial improvement over the aforedescribed prior art vis-a-vis the rate and/or selectivity of the epoxidation reaction, particularly when employing the hydrogen peroxide as a commercially available dilute aqueous solution, there has been a further continuing search for alternative compounds which can perform the same function of these Co-catalyst II fluorinated oxygenated compounds but which are more readily available commercially at a substantially lower cost. The present invention was developed in response to this search also.